Nahum A. Medellin-Castillo

Kinetic study of the adsorption of nitroimidazole antibiotics on activated carbons in aqueous phase.

The adsorption kinetics of four nitroimidazoles, Dimetridazole (DMZ), Metronidazole (MNZ), Ronidazole (RNZ) and Tinidazole (TNZ), were studied on three activated carbons: two commercial carbons from Sorbo-Norit (S) and Merck (M) and a third prepared by chemical activation of petroleum coke (C). Experimental data of the corresponding adsorption kinetics were analyzed by applying pseudo-first and pseudo-second-order models and a general diffusion model. Application of pseudo-first and pseudo-second-order kinetic models verified the following: (i) The kinetic model used that better predicts the adsorption rates depends of both the adsorbent and adsorbate studied. (ii) Nitroimidazole adsorption rate decreases in the order MNZ>DMZ>RNZ>TNZ; therefore, in the case of MNZ, molecular size does not appear to be a determining factor in the process. (iii) Nitroimidazole adsorption rate on carbons increases in the order C<S<M, which is related to the increase in carbon hydrophobicity. Hence, in general, hydrophobic interactions appear to govern the kinetics of the adsorption process. Finally, a general diffusion model was applied that combines external mass transport and intraparticle diffusion, achieving an adequate fit to the experimental data. There are notable differences among the diffusivity values for the different nitroimidazoles that do not appear to be exclusively related to carbon textural parameters or adsorbate size. Therefore, adsorbent and adsorbate chemical characteristics are highly important to establish the adsorption mechanism of nitroimidazoles on activated carbons.

Removal of diethyl phthalate from water solution by adsorption, photo-oxidation, ozonation and advanced oxidation process (UV/H2O2, O3/H2O2 and O3/activated carbon)

The objective of this work was to compare the effectiveness of conventional technologies (adsorption on activated carbon, AC, and ozonation) and technologies based on advanced oxidation processes, AOPs, (UV/H(2)O(2), O(3)/AC, O(3)/H(2)O(2)) to remove phthalates from aqueous solution (ultrapure water, surface water and wastewater). Diethyl phthalate (DEP) was chosen as a model pollutant because of its high water solubility (1,080 mg/L at 293 K) and toxicity. The activated carbons showed a high adsorption capacity to adsorb DEP in aqueous solution (up to 858 mg/g), besides the adsorption mechanism of DEP on activated carbon is governed by dispersive interactions between π electrons of its aromatic ring with π electrons of the carbon graphene planes. The photodegration process showed that the pH solution does not significantly affect the degradation kinetics of DEP and the first-order kinetic model satisfactorily fitted the experimental data. It was observed that the rate of decomposition of DEP with the O(3)/H(2)O(2) and O(3)/AC systems is faster than that with only O(3). The technologies based on AOPs (UV/H(2)O(2), O(3)/H(2)O(2), O(3)/AC) significantly improve the degradation of DEP compared to conventional technologies (O(3), UV). AC adsorption, UV/H(2)O(2), O(3)/H(2)O(2), and O(3)/AC showed a high yield to remove DEP; however, the disadvantage of AC adsorption is its much longer time to reach maximum removal. The best system to treat water (ultrapure and natural) polluted with DEP is the O(3)/AC one since it achieved the highest DEP degradation and TOC removal, as well as the lower water toxicity.

Medicinal plants used in the Huasteca Potosina, México.

ETHNOPHARMACOLOGICAL IMPORTANCE Medicinal plants have been a source of medicinal compounds since ancient times. This study documented the use of plant species in traditional medicine in the municipality of Aquismón, San Luis Potosí, México. MATERIALS AND METHODS Direct interviews were performed with inhabitants from Aquismón. The interviews were analyzed with two quantitative tools: (a) the informant consensus factor (ICF) that estimates the level of agreement about which medicinal plants may be used for each category and (b) the relative importance (RI) that determines the extent of potential utilization of each species. RESULTS A total of 73 plant species with medicinal purposes, belonging to 37 families and used to treat 52 illnesses and 2 cultural filiations were reported by interviewees. Nineteen mixtures with medicinal plants were reported by the interviewers. Matricaria recutita was the most used plant for combinations (five mixtures). The results of the ICF showed that diseases of the digestive and respiratory systems had the greatest agreement. The most versatile species according to their RI are Ruta graveolens, Tagetes erecta, Ocimum basilicum and Erigeron karwinskianus. CONCLUSION This study demonstrates that plant species play an important role in healing practices and magical-religious rituals among inhabitants from Huasteca Potosina. Further studies with medicinal flora, including mixtures, from Aquismón are required for the experimental validation of their traditional uses.

Kinetic Modelling of Naphthalenesulphonic Acid Adsorption from Aqueous Solution onto Untreated and Ozonated Activated Carbons

The adsorption rate of 1-naphthalenesulphonic (NS), 1,5-naphthalenedisulphonic (NDS) and 1,3,6-naphthalenetrisulphonic (NTS) acids onto activated carbon (AC) was studied in this work. In addition, the effect of oxidizing the AC with ozone on the rate of adsorption was investigated. The adsorption equilibrium data as well as the concentration decay data for the naphthalenesulphonic acids (NSAs) were obtained in a batch adsorber. The Freundlich, Langmuir and Prausnitz–Radke isotherms were fitted to the experimental adsorption equilibrium data when it was found that the Prausnitz–Radke isotherm gave the best fit. The experimental concentration decay data were interpreted via a diffusional model which considered the adsorption rate at a surface site, external mass transport and intraparticle diffusion. The results revealed that intraparticle diffusion was the controlling mechanism in the diffusional model and that this model predicted the experimental data satisfactorily. The effective diffusion coefficients of the NSAs could be estimated using the tortuosity factor equation together with tortuosity factors for the ACs ranging from 3.7 to 5.5.

Synthesis of α-Alumina Nano-Onions by Thermal Decomposition of Aluminum Formate

A simplified route to prepare α-Al2O3 nano-onions and alumina powders with an excellent surface area through the thermal decomposition of aluminum formate (Al(O2CH)3) precursor is proposed. The calcined powders were characterized by infrared and 13C MAS NMR spectroscopy. Coordination numbers and chemical interactions were determined by 27Al MAS NMR spectroscopy. The 27Al MAS NMR spectra showed the presence of η-Al2O3 at 1000°C, and the transformation to α-Al2O3 at 1100°C. The spectral data also showed that while the precursor contained 6-coordinated aluminum ions, four-, five-, and six-coordinated aluminum species were present after calcination at 400°C. SEM images and BET measurements of α-Al2O3 revealed aggregated particles with a specific surface area of 118 m2/g. A nano-onion structure of α-Al2O3 was evident from the HRTEM image.

BIOADSORCIÓN DE PLOMO (II) PRESENTE EN SOLUCIÓN ACUOSA SOBRE RESIDUOS DE FIBRAS NATURALES PROCEDENTES DE LA INDUSTRIA IXTLERA (Agave lechuguilla Torr. y Yucca carnerosana (TREL.) MCKELVEY)

El plomo ha sido reconocido como uno de los metales mas toxicos por su efecto negativo sobre el ambiente. En el presente trabajo se evaluo el uso potencial de residuos de Agave lechuguilla Torr. (lechuguilla) y Yucca carnerosana (Trel.) McKelvey (yuca) procedentes de la industria ixtlera para remover iones Pb (II) presentes en solucion acuosa. Los datos del equilibrio de bioadsorcion mostraron que al aumentar el pH de la solucion de 2.0 a 5.0, la capacidad de bioadsorcion de ambos materiales se incrementa. Este efecto se explico considerando que la carga superficial negativa de estos materiales es mayor al aumentar el pH y por ello se favorece la remocion de Pb (II). El efecto de la temperatura de la solucion en las isotermas de bioadsorcion, expuso la naturaleza endotermica del proceso. La energia libre de Gibbs y la entropia calculada (ΔG° y ΔS°) indicaron la espontaneidad de la bioadsorcion y la afinidad del Pb (II) en solucion por los bioadsorbentes, respectivamente. La variacion de las capacidades de bioadsorcion de la lechuguilla y la yuca se atribuyo a la diferencia en el contenido de sitios acidos y lignina, lo que condujo a la presencia de diversos mecanismos de bioadsorcion. En ambos materiales, la bioadsorcion de Pb (II) ocurre por los mecanismos de interacciones π-cation, atracciones electrostaticas e intercambio ionico; ademas en el caso de la lechuguilla se evidencio un proceso de microprecipitacion.El plomo ha sido reconocido como uno de los metales mas toxicos por su efecto negativo sobre el ambiente. En el presente trabajo se evaluo el uso potencial de residuos de Agave lechuguilla Torr. (lechuguilla) y Yucca carnerosana (Trel.) McKelvey (yuca) procedentes de la industria ixtlera para remover iones Pb (II) presentes en solucion acuosa. Los datos del equilibrio de bioadsorcion mostraron que al aumentar el pH de la solucion de 2.0 a 5.0, la capacidad de bioadsorcion de ambos materiales se incrementa. Este efecto se explico considerando que la carga superficial negativa de estos materiales es mayor al aumentar el pH y por ello se favorece la remocion de Pb (II). El efecto de la temperatura de la solucion en las isotermas de bioadsorcion, expuso la naturaleza endotermica del proceso. La energia libre de Gibbs y la entropia calculada (ΔG° y ΔS°) indicaron la espontaneidad de la bioadsorcion y la afinidad del Pb (II) en solucion por los bioadsorbentes, respectivamente. La variacion de las capacidades de bioadsorcion de la lechuguilla y la yuca se atribuyo a la diferencia en el contenido de sitios acidos y lignina, lo que condujo a la presencia de diversos mecanismos de bioadsorcion. En ambos materiales, la bioadsorcion de Pb (II) ocurre por los mecanismos de interacciones π-cation, atracciones electrostaticas e intercambio ionico; ademas en el caso de la lechuguilla se evidencio un proceso de microprecipitacion